For various reasons associated in particular with better comfort during their use (softness, emollience and the like), current cosmetic compositions are usually in the form of an emulsion of the oil-in-water (O/W) type consisting of an aqueous dispersing continuous phase and an oily dispersed discontinuous phase, or of an emulsion of the water-in-oil (W/O) type consisting of an oily dispersing continuous phase and an aqueous dispersed discontinuous phase. O/W emulsions are the ones most sought in the cosmetics field, since they comprise an aqueous phase as external phase, which gives them a fresher, less greasy and lighter feel than W/O emulsions when they are applied to the skin.
The emulsions are generally stabilized with suitable emulsifying surfactants, which, by virtue of their amphiphilic structure, become positioned at the oil/water interface and thus stabilize the dispersed droplets. However, these emulsifiers have the drawback of being penetrating and potentially irritant to the skin, eyes and the scalp, especially in the case of individuals with sensitive skin.
In addition, such emulsions may have insufficient cosmetic and physicochemical properties (oily feel, instability over time). Increasing the surfactant content generally does not solve the problems mentioned. The required stability is not always achieved and the cosmetic properties are not improved (waxy, heavy feel, lack of freshness on application). Moreover, as mentioned above, it is also not recommended to use an excessively high content of surfactant for reasons of harmfulness.
One solution for overcoming the instability of O/W emulsions (creaming and phase separation) consists in introducing into the emulsion thickeners whose function is to create, in the aqueous phase, a gelled matrix that serves to set the oily droplets and ensures mechanical maintenance of the whole emulsion. Moreover, it has been envisaged to replace the surfactants with hydrophilic polymers comprising in their chain a hydrophilic portion and a hydrophobic portion, such as copolymers of C10-C30-alkyl acrylate and of acrylic or methacrylic acid, for instance the product “Pemulen TR2” sold by the company Goodrich, or with hydrophilic polymers derived from 2-acrylamido-2-methylpropanesulphonic acid (AMPS), as described in document EP-A-815 844.
However, emulsions stabilized with hydrophilic polymers may have a coarse feel. To improve the softness of these emulsions, the Asssignee has sought to incorporate therein compounds that afford softness, and especially elastomeric organopolysiloxanes (also known as silicone elastomers), such as the products sold by Shin-Etsu under the name KSG. However, the Assignee has found that when these elastomeric organopolysiloxanes are introduced in large amount, and especially in an amount of greater than 1% (of active material); they have a tendency to destabilize the emulsion containing the hydrophilic polymer.
One object of the invention is the provision of oil-in-water (O/W) emulsions that show good cosmetic properties (softness), which are stable, i.e. which do not undergo a phase separation and do not release oil, irrespective of the amount of silicone elastomer contained in the emulsion.